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GATE 2026 · CS2 - Afternoon
Programming & Data StructuresStacks & QueueshardMSQ2 marks
Consider a stack S and a queue Q. Both of them are initially empty and have the capacity to store ten elements each. The elements 1, 2, 3, 4, and 5 arrive one by one, in that order. When an element arrives, it is assigned either to S (pushed on S) or to Q (enqueued to Q). Once all the five elements are stored, the output is generated in two steps. First, stack S is emptied by popping all elements. Then queue Q is emptied by dequeueing all elements. The output obtained by following this process is 4 3 1 2 5. Given the output, the objective is to predict whether an element was assigned to S or Q. Which of the following options is/are possible valid assignment(s) of the elements? Note: In the options, the notation xS denotes that element x was assigned to S and yQ denotes that element y was assigned to Q.

Select every correct option.

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